Silicon (Si)-containing films are used for a wide variety of applications in the semiconductor industry. Si-containing films include films such as epitaxial Si, polycrystalline Si (poly-Si), amorphous Si, epitaxial silicon germanium (SiGe), silicon germanium carbide (SiGeC), silicon carbide (SiC), silicon nitride (SiN), silicon carbonitride (SiCN), and silicon carboxide (SiCO). As circuit geometries shrink to ever smaller feature sizes, lower processing temperatures are preferred, for example because of introduction of new materials into semiconductor devices and/or reduction of thermal budgets for shallow implants in source and drain regions. Moreover, it is evident that non-selective (blanket) and selective deposition of Si-containing films will be needed for future devices.
Epitaxial Si deposition is a process where the crystal lattice of the bulk Si is extended through growth of a new Si-containing film that may have a different doping level than the bulk. Matching target eptaxial film thickness and resistivity parameters is important for the subsequent fabrication of properly functioning devices. Prior to depositing a Si-containing film, e.g., epitaxial Si or epitaxial SiGe films, on a Si substrate, it may be required to remove a native oxide layer from the surface of the substrate in order to prepare a proper starting growth surface (i.e., a seed layer) to deposit a high quality epitaxial film on. A native oxide layer, which may be a few to several angstrom (1 Å=1×10−10 m) thick, for example, forms easily on clean Si surfaces when exposed to an oxygen-containing environment (e.g., air), even at room temperature and atmospheric pressure. If the substrate is not cleaned prior to depositing a Si-containing film on the substrate, i.e., all oxygen and other contaminants have not been properly removed from the substrate surface, then the Si-containing film subsequently deposited on the substrate may not grow epitaxially and may contain defects that can lead to a high leakage current through the film and cause the microelectronic device to not perform optimally.
Similarly, a poly-Si film can be deposited directly on a poly-Si film to form an electrical contact. However, because other processing typically occurs between the poly-Si deposition steps, the substrates (wafers) can be removed from the processing system between the deposition steps, in which case a native oxide layer can form on the substrates. If the native oxide layer is not removed prior to depositing the poly-Si film, the resulting contact can have high electrical resistance and/or other undesirable properties.
It may also be necessary to remove a native oxide layer from a substrate, for example, prior to depositing a high dielectric constant (high-k) film on the substrate, where the high-k film is a part of a gate stack. Examples of high-k films include HfO2, HfSiOx, HfSiOxNy, ZrO2, ZrSiOx, and ZrSiOxNy. The presence of an oxide layer can reduce the effective dielectric constant of the gate stack since the oxide layer normally has a lower dielectric constant than the high-k film. Thus, a higher dielectric constant and higher level of control over the overall dielectric constant can be achieved if the oxide layer is effectively removed before depositing a high-k film.
Traditionally, high-temperature annealing at or above 900° C. in a hydrogen atmosphere has been used in (vertical) batch processing systems to remove a native oxide layer from substrates and clean the substrates of other impurities prior to a deposition process. However, such a high-temperature process does not meet current or future thermal budget needs for many advanced processes, which can prevent their integration into device manufacturing process flows. For example, current gate lengths and modern microelectronic structures limit devices to a reduced thermal budget.
Plasma processing has been found to allow lowering of the substrate temperature during processing and thus offers an alternative to high-temperature annealing in a hydrogen atmosphere. However, exposure of the substrate to a plasma source can damage the substrate as a result of the interaction of excited species in the plasma with the substrate. Another oxide removal method is based on hydrogen fluoride (HF), but the use of HF can result in incomplete oxide removal and unwanted erosion of the substrate and various films on the substrate.